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Three experimental grazing trials were conducted to
explore the hypothesis that in the Klamath Basin, a higher
level of selenium supplementation is necessary than those
proven adequate elsewhere. Two forage species were
investigated: Festuca arundinaeca and Agropyron repens, in
0.61 hectare plots, both grown in a selenium deficient soil
area. Selenium treatments were offered free choice in a
salt-mineral mixture, to growing beef heifers.
In Experiments I and II the animals were rotationally
grazed between the grasses, while in Experiment III they
were grazed by forage type. Average total weight gain was
used to measure performance, and selenium status was
monitored by whole blood analysis. Selenium was
supplemented at levels of 0, 25, 50, and 100 ppm added to
the salt-mineral mixture in Experiment I; 0, 25, 50, 100,
200, and 300 ppm in Experiment II; and 0, 200, and 400 ppm
in Experiment III.
In Experiment I selenium supplementation increased
(P<.05) weight gains of grazing heifers. Linear regression
indicated that a higher level of selenium supplementation
might result in increased (P<.02) weight gains. Only the
highest level of supplementation (300 ppm) resulted in an
increase (P<.05) in weight gain in Experiment II.
Experiment III results indicated a increase (P<.01) in
weight gain from supplementation of selenium at both the
200 and 400 ppm levels on wheatgrass, but no added increase
above the 200 ppm level. There was no increase in weight
gain on tall fescue. Whole blood selenium levels closely
paralleled the level of selenium supplementation. No toxic
or detrimental effects were observed from selenium
supplementation at any level.
The results substantiate the concept that adequate
selenium supplementation depends on a number of factors,
including soil and plant levels, and forage type and
demonstrate problems inherent in using a single level to
cover variable conditions. In the Klamath situation, the
approved level of 20 ppm selenium in a salt-mineral mix
proved insufficient for maximum performance.